In ITU-R (International Telecommunication Union Radio communication sector), a standardization task for IMT (International Mobile Telecommunication)-Advanced (i.e., the next-generation mobile communication system after the 3rd generation) is being in progress. IMT-Advanced sets its goal to support IP (Internet Protocol)-based multimedia service at the data transfer rate of 1 Gbps in the stop and slow-speed moving states and at the data transfer rate of 100 Mbps in the fast-speed moving state.
3GPP (3rd Generation Partnership Project) is preparing for a system standard to satisfy the requirements of IMT-Advanced. That is LTE-Advanced improved from LTE (Long Term Evolution) based on OFDMA (Orthogonal Frequency Division Multiple Access)/SC-FDMA (Single Carrier-Frequency Division Multiple Access) transmission schemes. LTE-Advanced is one of the strong candidates for IMT-Advanced. Relay station technology is included in the major technology of LTE-Advanced. Relay station is a device which relays a signal between a base station and a user equipment. It is used for extending a cell coverage and improving a throughput of the wireless communication system.
Relay stations may be classified into several types according to their functions. For example, the relay stations may be classified into an L1 relay station (type 3 relay station), an L2 relay station (type 2 relay station), and an L3 relay station (type 1 relay station). The L1 relay station is a relay station having some additional functions along with AF (Amplify and Forward; forwarding after amplification). The L1 relay station amplifies a signal received from a base station or a user equipment and then transfers the amplified signal to the user equipment or the base station. The L2 relay station is a relay station having a scheduling function along with DF (Decoding and Forward; forwarding after decoding). The L2 relay station recovers information through processes, such as demodulation and decoding, for a signal received from a base station or a user equipment, generates a signal through processes, such as coding and modulation, and transfers the generated signal to the user equipment or the base station. The L3 relay station is a relay station having a similar shape as one cell. The L3 relay station supports call access, release, and mobility functions along with the functions of the L2 relay station. The L1, L2, and L3 relay stations perform different functions and uses different protocols when sending signals.
Furthermore, in the recent wireless communication system field, in a wireless communication system having a multi-cell structure, research is being carried out on schemes for improving the performance of a user equipment placed at the edge of a cell. In the wireless communication system having the multi-cell structure, active research is being carried out on coordinated multipoint transmission and receptions (CoMP) technology in which signals are transmitted through inter-cell mutual cooperation. According to CoMP, a user equipment, particularly, a user equipment placed at the edge of a cell can have improved signal sensitivity as well as an improved transmission power gain by communicating with a number of base stations.
If an entity participating in CoMP as a cooperative cell is the L3 relay station, the L3 relay station receives control information and data transmitted by a base station, performs decoding according to a protocol architecture, encodes the control information and data according to its own protocol architecture, and sends them to a user equipment. In this case, scheduling information and the like which are related to a transport block transmitted by the base station may be changed by the L3 relay station because of a difference in the channel state, the scheduling strategy and so on between the base station and the L3 relay station. Accordingly, the user equipment may have difficulties in the reception, decoding and so on of a signal according to CoMP owing to a difference between the signal received from the base station and the signal received from the L3 relay station.
Furthermore, if CoMP is performed in a wireless communication system including different and heterogeneous relay stations, different protocols may be used in the relay stations. Accordingly, a user equipment which receives signals from the heterogeneous relay stations and a base station according to CoMP may have a difficulty in performing decoding.